The technical field of the invention is that of integrated circuits and, in particular, memory circuits having programmable fuse elements, particularly antifuses.
Fuses and antifuses are used to personalize semiconductor devices to meet specific integrated circuit requirements. To personalize a semiconductor device with fuses, some of the available fuses are blown by a laser or other means to make the desired changes to the device and its associated circuits. Fuses are blown to make a previously closed connection open. Antifuses are also used to personalize semiconductor devices. Antifuses are devices that perform the opposite function of a fuse. When a sufficient voltage is applied across an antifuse structure, the structure becomes permanently shorted, and an electrical connection is made. Thus, antifuses are xe2x80x9copenxe2x80x9d and unconnected until they are xe2x80x9cprogrammedxe2x80x9d to provide a closed connection.
In this application, the term xe2x80x9cfuse elementxe2x80x9d will be used to cover both fuses and antifuses, both of which can be used with the latch device and programming circuits of the present invention. The term xe2x80x9cfuse latchxe2x80x9d will be used to reference a latch device that can be used for both fuses and antifuses.
Antifuse structures are made by stressing an insulating medium between two conductors. Programming these structures is most reliable if current levels during programming and during use are kept under a safe level to prevent premature wear out of the fused filament. A means for limiting the programming current is therefore needed to prevent overstressing the antifuse element during programming.
It is desirable to program many antifuses in parallel to reduce test time. However, with several fuses programmed in parallel, the lowest resistance fuse tends to shunt current away from other fuses that may need the current to program successfully. Thus, a means for programming fuses in parallel with a uniform amount of programming current passing through each fuse is needed.
Related art fuse latches also lacked a means for determining if an antifuse programmed successfully, and for testing the resistance margin over what resistance value is required by the fuse latch for proper sensing. Another problem with high-trip point fuse latches in the related art is their sensitivity to electrical disturbances, which sometimes cause soft error upsets or failures of the fuse latch. A means for adjusting the resistive trip point of the fuse latch and for improving the immunity of the fuse latch to soft error failures is therefore needed, particularly after the latch is set.
A latch device is provided having a variable resistive trip point and controlled current programming. The latch device has a trip point current control element that controls an amount of current passing from a voltage source into the latch circuit, thereby varying the resistive trip point of the latch device. The trip point current control element in the disclosed embodiment is a PFET that has its gate connected to a trip point current reference and its source and drain connected between the voltage source and the latch circuit.
The latch device also has a programming current control element that controls an amount of programming current passing through the fuse element during programming. The programming current control element in the disclosed embodiment is an NFET that has its gate connected to a programming current reference and its source and drain placed in the path of the programming current.
The trip point current reference and the programming current reference are provided by reference circuits having a plurality of selectable inputs that operate to change the current references binarily. The reference circuits use current mirror technology to set the current flows through the latch device at predictable levels.
The application also discloses an integrated circuit in which a plurality of fuse latch devices are connected together in parallel such that the same trip point current reference and programming current reference are supplied to each latch device. A global trip point control circuit and a global programming current control circuit provide the trip point current reference and the programming current reference, respectively.
Generally, the present invention provides a latch device having a variable resistive trip point, comprising:
a voltage source;
an adjustable trip point current reference;
a latch circuit having a fuse latch output; and
a trip point control element, said trip point control element being operable to control the amount of current passing through said latch circuit based on said adjustable trip point current reference, thereby providing the latch device with a variable resistive trip point.
The present invention further provides a fuse element programming circuit having controlled current programming, comprising:
a fuse element; and
a current control device connected to said fuse element, said current control device being controlled by a programming current reference to limit an amount of programming current passing through the fuse element, the programming current reference being adjustable.
The present invention additionally provides an integrated circuit comprising:
a global trip point control circuit that provides an adjustable trip point current reference; and
a plurality of fuse latch devices, each fuse latch device comprising a latch circuit having a fuse latch output and a trip point control element, said trip point control elements being connected in parallel to said adjustable trip point current reference and being operable to control an amount of current passing through each of said latch circuits based on said adjustable trip point current reference.
The present invention also provides an integrated circuit comprising:
a global programming current control circuit that provides an adjustable programming current reference; and
a plurality of fuse latch devices, each fuse latch device comprising a fuse element and a programming current control device, said programming current control devices being connected in parallel to said adjustable programming current reference and being operable to control an amount of programming current passing through each of said fuse elements based on said adjustable programming current reference.